1. Field of the Invention
This invention relates to an implant prosthesis adapted to construct artificial bones and artificial tooth for orthopedic surgery used for restoring the bone function and joint function of hands and feet lost by diseases and accidents or for restoring the artificial tooth root adapted for reconstruction of the tooth lost due to old age and diseases. This invention also relates to a method of producing the same.
2. Prior Art
In recent years there has been reported a remarkable development of implantology, and various artificial organs such as artificial heart, artificial blood vessel, artificial lungs play a brilliant role in medical circles.
Particularly, artificial bones for use in artificial joints for recovering the lost joint function are widely used, while the artificial root of a tooth is highlighted in the field of dental treatment.
Because endosseous type implant prosthesis of the kind described such as the artificial joint, artificial bone, artificial tooth root require high strength, stainless steel and cobalt-chromium alloy have conventionally been used for the implant prosthesis materials. But the problem arose that the metal material rusts within a living body to dissolve metallic ion to produce advserse effects on the bone cell and in the worst case the implant material may break.
In an attempt to solve the problem of affinity of this metal prosthetic material with the tissue of a living body, a ceramic material such as alumina has come to be introduced and has found its application in an artificial knee joint and the like. The ceramic material is excellent in its affinity with the bone tissue and is united into one body with the bone in the human body, with not always unexceptional cases of splended restoration in function. But when the material was used under the load of walking or the like, it failed to obtain sufficient fixation to the bone, with no small number of cases of loosening and revision or redoing. In an effort to solve the problem of endosseous fixation of the ceramic implant prosthesis material of the kind described above, coating of the implant with calcium phosphate based material by plasma spraying has been developed and is discussed in Japanese patent publication No. 46911/1984.
It is well known that calcium phosphate based materials (hereinafter referred to as apatite) such as hydroxyapatite, tricalcium phosphate are chemically united with bones and also a metal implant material having a coating applied thereover by thermal spraying is already commercially available. The above-disclosed art also uses thermal spraying of apatite or a mixture of apatite and ceramic powder onto the surface of the ceramic implant or forms a ceramic layer over the ceramic implant by thermal spraying and a further apatite coating thereover once more.
However, although the prior art mentioned above is an effective art, yet raises serious problems in point of practical application. One of the problems is concerned with the adhesive force of the apatite thermally sprayed layer relative to a foundation. According to the thermal spraying, as is generally the case, the spraying secures an adhesive force of the thermally sprayed layer by toughening the foundation by sandblasting. Namely, thermal spraying depends solely upon mechanical anchoring for the adhesive force of the thermally sprayed layer relative to the foundation, and accordingly, unless the foundation has a certain degree of irregularities on the surface thereof, the thermally sprayed layer cannot stick to the foundation. Although the artificial joint and bone are made of a high strength ceramic material such as alumina, zirconium dioxide, yet the mentioned ceramic materials are of high strenghth and are at the same time very hard and it is difficult to roughen the surface of the ceramic material by use of sandblast. Also, the sandblast forcefully carried out cannot provide a sufficient degree of roughness and the thermal spraying of the apatite layer over the thus toughened surface cannot provide an adhesive force which can stand the use of the layer as an implant prosthesis.
On the other hand, the ceramic material is fragile and susceptible to scratches. Even if the scratches are small, they may cause a great reduction in the strength of the material. Sandblasting is an effective means for toughening the surface of a metal material which is a ductile material, but is a risky means which brings about reduced strength relative to the ceramic material. The same is also the case with means other than the blasting for forming a roughened surface. It is an established fact that the deflection strength of monocrystalline alumina is reduced to half or less by small scratches and toughening. The second problem of the prior art mentioned above is the disadvantages of reduction in the strength of the ceramic substrate of the kind thus described above.